From: Jan Svitok <jan.svitok@...>
Date: 2006-11-24T19:50:14+09:00
Subject: Re: Problems with String#hash

On 11/24/06, George Moschovitis <george.moschovitis@gmail.com> wrote:
> Dear devs,
>
> I am facing a very NASTY problem with String#hash
>
> Here is the same code that I run on 3 different computers:
>
> root@kosh:~ # irb
> irb(main):001:0> "User".hash
> => 690465448
> irb(main):002:0> VERSION
> => "1.8.2"
>
> C:\Documents and Settings\drak>irb
> irb(main):001:0> "User".hash
> => 690465448
> irb(main):002:0> VERSION
> => "1.8.4"
>
> http://tryruby.hobix.com/
>  Interactive ruby ready.
> >> "User".hash
> => 690465448
> >> VERSION
> => "1.8"
>
> root@victory:~# irb
> irb(main):001:0> "User".hash
> => -1457018200
> irb(main):002:0> VERSION
> => "1.8.4"
>
> Please nottice that on the last case I get a different result! Any
> idea why this happens?
>
> thanks in advance for any help!
>
> George.

string.c:851
int
rb_str_hash(str)
    VALUE str;
{
    register long len = RSTRING(str)->len;
    register char *p = RSTRING(str)->ptr;
    register int key = 0;

#if defined(HASH_ELFHASH)
    register unsigned int g;

    while (len--) {
	key = (key << 4) + *p++;
	if (g = key & 0xF0000000)
	    key ^= g >> 24;
	key &= ~g;
    }
#elif defined(HASH_PERL)
    while (len--) {
	key += *p++;
	key += (key << 10);
	key ^= (key >> 6);
    }
    key += (key << 3);
    key ^= (key >> 11);
    key += (key << 15);
#else
    while (len--) {
	key = key*65599 + *p;
	p++;
    }
    key = key + (key>>5);
#endif
    return key;
}

I suspect those #ifdefs. See your config.h what's compiled in.